Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $92.95   6.714%   $99.1907   $99.19   $99.20   $99.20  
  Purchase #2 $248.42   8.543%   $269.6425   $269.64   $269.65   $269.60  
  Purchase #3 $126.55   4.694%   $132.4903   $132.49   $132.50   $132.50  
  Purchase #4 $112.33   8.470%   $121.8444   $121.84   $121.85   $121.80  
  Purchase #5 $11.99   12.127%   $13.444   $13.44   $13.45   $13.40  
  Purchase #6 $107.97   4.767%   $113.1169   $113.12   $113.10   $113.10  
  Purchase #7 $31.60   4.840%   $33.1294   $33.13   $33.15   $33.10  
  7 purchase totals = $731.81       $782.8582   $782.85   $782.90   $782.70